As for example shown in FIG. 1, a milling cutter of a crank shaft miller comprises a cutter body 1 which is formed in an approximate ring shape, and a plurality of cutter tips 2a, 2b, and 2c which are positioned at appropriate intervals along both side edges of the inner circumferential surface of the cutter body 1 and are fixedly attached thereto. The shapes of the above described cutter tips 2a, 2b, and 2c, as seen from their fronts and backs, are formed as approximate parallelograms, and cutting edges are formed along their ridge lines at a plurality of corners and in the neighborhood thereof. Per se known techniques related to the above described type of milling cutter are, for example, disclosed in Patent Document #1.    Patent Document #1: Japanese Laid-Open Patent Publication 2000-354905.
Now, with a milling cutter of the structure described above, since it is necessary to perform a large amount of cutting when performing machining processing (for so called rough machining) of a side surface of a counter weight and the contiguous outer circumferential surface of a pin journal, accordingly two cutter tips of the same shape (2a, 2b) are used by being fixedly attached to the cutter body 1 in attitudes so that one of the long sides of the cutter tip 2a faces the outer circumferential surface of the pin journal, while one of the long sides of the other cutter tip 2b faces the side of the counter weight, and moreover so that the track of the cutting by the other cutter tip 2b described above is superimposed upon the track of cutting by the one cutter tip 2a described above. In the following explanation, for the sake of convenience, that cutter tip 2a which is mounted in such an attitude that one of its long sides faces the outer circumferential surface of the pin journal is termed the “horizontal outer circumferential cutter tip”, while that cutter tip 2b which is mounted in such an attitude that one of its long sides faces the side surface of the counter weight is termed the “vertical outer circumferential cutter tip”. Moreover, when performing a small amount of further cutting upon the site described above (for so called finishing machining), a single cutter tip 2c which has the same shape as each of the two cutter tips 2a and 2b described above is used by being fixedly attached to the cutter body 1 in such an attitude that one of its long sides faces the side surface of the counter weight. In the following explanation, for the sake of convenience, this cutter tip 2c will be termed the “side cutter tip”.
Thus, two each of the horizontal outer circumferential cutter tip 2a, the vertical outer circumferential cutter tip 2b, and the side cutter tip 2c (i.e. a total of six cutter tips) constitute one set of cutter tips; and a plurality of these cutter tip sets (2a, 2b, and 2c) are fixedly attached at appropriate intervals along both side edges of the inner circumferential surface of the cutter body 1, with the task of machining the crank shaft being performed principally by using the acute angled corners at four spots upon each of these cutter tips (2a, 2b, 2c) (the frequency of using the acute angled corners is approximately twice the frequency of using the obtuse angled corners). And, when one of these acute angled corners suffers damage due to the cutting task, the fixing direction of that one of these cutter tips (2a, 2b, 2c) to the cutter body 1 is changed over, in order to continue the cutting task using its other acute angled corners which are not damaged.
However since, no matter how many of the cutter tips (2a, 2b, 2c) may be reversed in fixing direction, the frequency of use of the acute angled corners is approximately twice the frequency of use of the obtuse angled corners, accordingly it unavoidably becomes necessary to change over some of the cutter tips (2a, 2b, 2c) for new ones even though their obtuse angled corners may not be completely worn out, and therefore it has not been possible to avoid the problem that the running cost becomes very substantial.